Once a solid Tory stronghold, it was snatched by Labour in 1997, and has now been turned into a three-way marginal by the ­rising strength of the Green party, whose candidate is their leader and current MEP, Caroline Lucas. They already have nine councillors to the Tories' six and Labour's five – and the latest poll puts Lucas eight points ahead of her nearest rival. The result: a trickle of headlines about the prospect of a small Green revolution, and rising local excitement that's not hard to pick up (try the anarchist bookshop on London Road – when I popped in, they could barely contain themselves).

"One more Tory MP, one more Labour MP – what difference is that going to make?" says Lucas. "The first Green MP, I think, would have a far greater effect." To that end, she is fighting hard, and doing as well as you'd expect among people who live in Brighton's bohemian centre – though much of the battle will be fought in the seat's more suburban patches, split between traditionally ­Labour-supporting estates and more Tory-favouring areas, with extensive gardens.

Aside from the Greens' chances, there are plenty of other reasons to be interested. Much is being made of the all-women field. The impressive Labour hopeful, Nancy Platts (who takes the place of ­retiring MP David Lepper), makes pointed ­mention in her campaign bumf of her ­opposition to the Iraq war, Trident and ID cards, and she needs no encouragement to talk about her trade unionism. Tory Charlotte Vere, meanwhile, is David Cameron's brand of Conservatism incarnate: a one-time internet entrepreneur who recently landed herself in trouble when she tweeted a link to a blog comparing the Greens to the BNP.

So, things may yet get nasty – though when I meet Lucas at a Green campaign stall near Brighton's Open Market, she's all optimism and bonhomie, pushing a petition on reducing local speed limits to 20mph, and talking about her left-of-Labour pitch to voters. "There is a demographic here that likes to think of Brighton as being ahead of the game – being more progressive," she says. We'll soon see whether it is.